This invention relates to water-in-oil emulsions of hydrophobe association polymers and a method for the preparation thereof.
As taught in Encyclopedia of Polymer Science and Technology, Interscience Publishers, Vol. I, 192 (1964), it is known that the viscosity of an aqueous medium is increased by the addition of a water-soluble polymer. Such water-soluble polymers include polyacrylamide, acrylamide/acrylic acid copolymer, sodium polyacrylate, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, polysaccharide as well as naturally occurring gums such guar gum and chemically modified gums such as hydroxypropyl guar gum. As a result of this thickening capability, there are many existing, as well as potential, industrial applications for aqueous media thickened with such water-swellable polymers. As taught in U.S. Pat. No. Re. 28,474, it is often desirable to prepare such polymers in the form of water-in-oil emulsions which are then inverted into aqueous media at the time of use.
Unfortunately, however, the aforementioned conventional water-soluble polymers suffer from many serious deficiencies or limitations in actual use in such industrial applications. For example, in many commercial applications, the polymers are exposed to shearing conditions which physically degrade them to lower molecular weight polymers thereby causing reduction of viscosity for the aqueous media containing them. Also, aqueous media containing the ionic water-soluble polymers exhibit substantial viscosity reduction when electrolytes are introduced into the media as is common in many applications, particularly in enhanced oil recovery. Finally, exposure of the aqueous media to high temperatures as is necessary for many applications normally causes a reduction in viscosity.
In attempts to overcome some of the aforementioned deficiencies of the conventional water-soluble polymers, it has been a common practice to cross-link the polymer in order to improve resistances to thermal as well as shear degradation. See, for example, U.S. Pat. No. 3,247,171. Such attempts have generally not been successful. More recently, as taught in U.S. Pat. No. 3,984,333, an aqueous medium has been thickened by dissolving a block copolymer having water-soluble blocks and water-insoluble blocks in the aqueous medium. While such block copolymers apparently exhibit reasonably good resistance to shear degradation, such polymers are difficult and often impractical to prepare. More importantly, such polymers do not exhibit significant tolerance of electrolytes normally present in the aqueous media to be thickened.
More recently, it has been discovered, as taught in U.S. Pat. No. 4,432,881, to employ dydrophobe association copolymers of water-soluble ethylenically unsaturated monomers and hydrophobic ethylenically unsaturated copolymers in combination with nonionic surfactants in order to overcome many of the aforementioned deficiencies of the conventional water-soluble polymers and recently developed substitutes therefore. Unfortunately, such hydrophobe association polymers could not be readily made in the form of emulsions and thus were not as easily handled and utilized as is desired for many applications.